The Shells of Infertile Eggs

[DameHillDucks]

Hi everyone,

We keep ducks, and have noticed a phenomenon I just haven't heard a lot about. Not infrequently, we get a "striped" egg. Just looking at the egg, it doesn't seem different from any other. Thickness is good, size/shape is normal. We noticed these when my sister began blowing out some duck eggs, and then when we were candling during incubation.

If you shine a light through the egg, you can see a bit of patterning in the shell - darker and lighter striping. The first time we incubated, we found that NONE of these eggs developed an embryo. I did some research and found an article (which I'm currently trying to find again!) saying that most of the time these eggs are indeed infertile.

My question is this: Has anyone else noticed these eggs? Does it suggest a deficiency in diet or a problem with the bird's health, or is it just a random occurrence or normal sign of infertility?

Thanks everyone! I haven't posted a lot yet, but this form has always been an incredible wealth of information for me.